McIntosh C45 "Tone Bypass" mode question

The C45 was apparently made with SACD and DVD-A in mind. My question is, when in "Tone Bypass" mode the C45 assumes a "flat response range". I understand what this is, but in terms of how it relates to passing the full SACD and DVD-A ranges through the device, does the C45 depart from its technical spec of 20-20khz and pass through, say, a signal of 4hz-50khz+ (which is where true SACD and DVD-A signal are)? C45 owners and EE engineers bring me some wisdom.

I'm not sure where you got your "20-20kHz" number, I assume from the basic specifications for the pre amp. Those numbers are stated by Federal mandate in order to make one component more comparable to another unit. After that the numbers are virtually without meaning.

No consumer amplifier - or pre amplifier, CD player, speaker, etc. - is strictly 20-20kHz with brickwall filters at both ends. The numbers are there for reference and comparison purposes only. All amplifiers (and pre amplifiers and other analog electronic devices) have a "power bandwidth" which essentially defines the total frequency response of the component - IOW the frequency extremes at which response has dipped sufficiently to be considered unusable for listening. The specification you gave for SACD would be a similar situation with the exception that digital is a bit flatter throughout its response than most analog circuits. Digital presents other issues as far as frequency response is concerned and filters are used more heavily at the extremes to avoid problems with a too high or too low response.

Which means the generic answer to your question is the Mac will pass whatever signal you feed it down to about 1Hz and up well beyond 100kHz.

The tone bypass has no effect on the frequency repsonse of the pre amplifier. Tone controls only modify (cut or boost) response within the given frequency range for any one control - "bass" might equal 500Hz and below while "midrange" might adjust roughly from 700-25000Hz. The frequency notations on the Mac are either the center frequencies for the three bands (controls) in the center or the "knee" frequency where the control turns over (takes effect) for the two frequency extremes. Since these are analog controls they do not suddenly start or stop at a specifc frequency but roll in or out gradually beyond their stated range.

When you select "Bypass" the tone controls are taken out of the signal path and flat response is returned - i.e., the controls are ineffective.

Further, in the Mac example, the tonals are taken completely out of the circuitry when bypassed or set to flat. Not everyone does this. repeat, the tonal circuits are completely removed fom the path, not mininalized or involved at all.

Tone controls with any expensive amp are generally no so much for the equipment as for compensating for room acoustics or ecoustics, I should say. Alternatively, they are there for those who are tone deaf in on way or another.

Over the last several months I've been comparing spec's between the C45 and the MP1. What I've concluded thus far is that the C45 offers several popular consumer features, cosmetics and boasting of its place in audio history while ARC is highly focused on publishing critical performance details of its product. Maybe this accounts for the significant price difference amongst other things. I am trying to determine the true guts of the C45 and match specs, but have only been able to access bits and pieces. My question of the day is the volume control. Is it analog, digital or some hybrid? in a true bypass shouldn't volume be analog and is the C45 truly offering analog volume control?

You should talk to Mac about your question since they know the ins and outs of their product better than anyone. However, I see nothing in their literature which would suggest the signal is converted to or stays in digital to pass through the vc.

I'm not certain of your reasoning for the bypass mode but I would say the signal can remain in the digital format if the pre amp is only dealing with digital signals. That would require either the elimination of the phono and other analog line inputs or the addition of a ADC (analog-digital converter) which isn't listed in any of the specifications for this pre amp. SACD is not passed in a pure digital format in this case so there is no need for a digital pass through on this pre amp.

Don't get hung up on specs. The value of specifications is for the manufacturer - to ensure unit to unit consitency. Anyone who argues the superiority of one component over another based on specs is not being totally honest with you. Yes, there are very good reasons for obtaining "good" specs and certain specs have more weight than others when it comes to the performance of the component. But for anyone who suggests this one spec tells you about the component's sound there will be another two or three who can successfully argue the value of a different spec or a different value for the same spec.

Reading specs on audio components is similar to reading wheel diameters and wheelbase in automotive magazines. Mac and ARC sound very different from one another - both very good in their own way but not at all similar if you listen carefully. IMO you would do yourself more good by determining what your priorities are in sound reproduction than by cruising through spec sheets.